Antistaling process and agent

ABSTRACT

The staling of leavened baked products such as bread is retarded by adding an enzyme with exoamylase activity to the flour or dough used for producing the baked product in question.

FIELD OF INVENTION

The present invention relates to a process for retarding the staling ofbread and similar baked products, as well as an agent for use in theprocess.

BACKGROUND OF THE INVENTION

Staling of baked products, principally bread, has been ascribed tocertain properties of the starch component of flour. Starch isessentially composed of amylose forming the core of starch granules andamylopectin forming the outer “envelope” of starch granules. Starchsuspensions have been observed to retrograde on standing to precipitatethe amylose which, by some, has been given as the explanation of thephenomenon of staling. Others have explained staling of bread in termsof the amylopectin chains in starch associating to cause a greaterrigidity of the bread crumb which is characteristic of stale bread.

It is generally recognized to be of some commercial importance to retardthe staling of baked products so as to improve their shelf-life.Retardation of the staling process may, for instance, be brought aboutby the addition of monoglycerides to dough. The antistaling effect ofthe monoglycerides may partly be ascribed to their ability to bind waterand partly to the formation of monoglyceride-amylose complexes whereinthe long hydrocarbon chain penetrates into the cavity of the amylosehelix and thereby stabilise the helical structure to preventretrogradation.

Enzymatic retardation of staling by means of α-amylases has also beendescribed, vide for instance U.S. Pat. No 2,615,810 and U.S. Pat. No.3,026,205 as well as O. Silberstein, “Heat-Stable BacterialAlpha-Amylase in Baking”, Baker's Digest 38(4), August 1964, pp. 66-70and 72. The use of α-amylase for retarding the staling of bread has,however, not become widespread. The reason for this is assumed to bethat the medium-molecular weight branched compounds, termedmaltodextrins (with 20-100 glucose units in the molecule), generatedthrough the hydrolytic action of α-amylases have a sticky consistency inthemselves resulting in the formation of a sticky or gummy crumb, andconsequently an unacceptable mouthfeel, of the baked product if theα-amylase is overdosed so that the maltodextrins are present inexcessive quantities.

It has previously been suggested to remedy the deleterious effects ofvery large doses of α-amylase added to dough by adding a debranchingenzyme such as pullulanase, cf. U.S. Pat. No. 4,654,216, the contents ofwhich are incorporated herein by reference. The theory behind theaddition of a debranching enzyme to obtain an antistaling effect whileconcomitantly avoiding the risk of producing a gummy crumb in theresulting bread is that by cleaving off the branched chains of thedextrins generated by α-amylase hydrolysis which cannot be degradedfurther by the α-amylase, the starch is converted to oligosaccharideswhich do not cause gumminess.

SUMMARY OF THE INVENTION

The present invention represents a different approach to the problem ofcrumb gumminess likely to result from the excessive use of α-amylase forretarding the staling of bread. Thus, the present invention relies onthe use of an enzyme which is capable of retarding the staling of bakedproducts but which does not hydrolyze starch into the above-mentionedbranched dextrins.

It has surprisingly been found that when the enzyme added to dough usedfor producing baked products is an exoamylase, an antistaling effect isobtained whereas the formation of a sticky or gummy crumb issubstatially avoided except at very high levels of the enzyme which alsogive rise to other deleterious effects likely to be discovered when thebaked products are subjected to quality control.

It was also found that by using exoamylase enzymes one avoids a certainsoftness and stickiness of the dough which is often encountered whenα-amylases, especially fungal α-amylases, are used for antistaling, andespecially if the α-amylase has been overdosed, even if only to a milddegree.

Accordingly, the present invention relates to a process for retardingthe staling of leavened baked products, which process comprises addingan enzyme with exoamylase activity to flour or dough used for producingsaid baked products. In the following, this enzyme is usually referredto as an “exoamylase”.

In another aspect, the present invention relates to a baked productproduced by the present process.

It will often be advantageous to provide the exoamylase in admixturewith other ingredients commonly used to improve the properties of bakedproducts. These are commonly known as “pre-mixes” and are employed notonly in industrial bread-baking plants/facilities, but also in retailbakeries where they are usually supplied in admixture with flour.

Hence, in a further aspect, the present invention relates to an agentfor improving the quality of leavened, in particular yeast leavened,baked products, which agent comprises an enzyme with exoamylase activityin liquid or substantially dry form. For the present purpose, such anagent will be termed a “bread improver” in the following descriptionalthough it will be understood that it may also be used for addition toother types of leavened baked products such as rolls, certain kinds ofcakes, muffins, buns, etc.

DETAILED DISCLOSURE OF THE INVENTION

Exoamylases are enzymes which hydrolyse (1−>4) α-glucosidic linkages instarch (and related polysaccharides) by removing mono- oroligosaccharide units from the non-reducing ends of the polysaccharidechains. The reducing groups liberated from the polysaccharide moleculemay be in the α- or β-configuration. Examples of exoamylases which areuseful for the present purpose are glucoamylase, β-amylase (whichreleases maltose in the β-configuration) and maltogenic amylase (whichreleases maltose in the α-configuration, but in contrast to α-amylasespredominantly produces maltotriose and maltotetraose and only minoramounts of higher oligosaccharides). The antistaling effect of addingexoamylase to dough is currently believed to be ascribable to theformation of sugars with a high water retention capacity which makes thebaked product in question appear fresh (soft) for longer periods of time(e.g. glucose, maltose, maltotriose and/or maltotetraose), as well as tothe modification of the native starch which reduces the tendency toretrogradation. Overdosing with the exoamylase resulting in crumbstickiness is less likely to occur because the formation of branchedmaltodextrins with 20-100 glucose units to which the stickiness may beascribed is, if not completely avoided, at least significantly lowerthan when using α-amylase.

The use of amylase (primarily α-amylase), invertase andpoly-saccharidase, as well as glucosidase (an exoamylase)) is suggestedin EP 136 158 and EP 136 159 for the preparation of cookies with a moistcrumb structure. Amylase is capable of forming crystallization-resistantsugar, which is able to bind water, from one or more ingredients in thedough resulting in the aforementioned moist crumb when the dough issubsequently baked. The cookies are indicated to be storage-stable.

It appears that the selection of the enzyme according to EP 136 158 andEP 136 159 is made with the object of obtaining a moist crumb structuredue to the formation of water-binding sugars from starch. With this endin view, pregelatinized starch is added to the dough to facilitateenzymatic hydrolysis into various sugar species. It further appears thatthe risk of obtaining a gummy crumb in the baked product throughaddition of too large an amount of a-amylase is not a problem to beavoided, but rather that moistness of the baked crumb is the end resultwhich the inventions disclosed in the above-mentioned EP applicationsintend to achieve. In fact, α-amylase which is known to produce crumbgumminess in leavened bread even when added in relatively low quantitiesis the preferred enzyme according to EP 136 159, the branchedmaltodextrins produced by the α-amylase apparently providingsatisfactory moisture characteristics to the cookies produced.

Contrary to this, the object of the present invention is to avoid asticky or gummy crumb in the baked product. The principal differencebetween the baked products disclosed in the EP applications and thoseproduced by the present process resides chiefly in the type of doughused to make the respective products. The products made by the presentprocess are leavened which implies that the gluten in the dough which iscomposed of layers of protein “sheets” joined to bimolecular layers oflipo- and phospholipoproteins is expanded by the carbon dioxide producedby the leavening agent (e.g. yeast) into a thin film which coagulates toa firm structure on heating. Starch serves to make the structure firmeras, on heating, it solidifies within the gluten structure. Thus, whenpreparing leavened baked products including an amylase enzyme to providethe antistaling effect, care must be taken to select one which resultsin a hydrolysis product with a good water retention capacity (e.g.maltose, maltotriose and/or maltotetraose) and sufficient modificationof the amylase and amylopectin to retard retrogradation so as to providea longer-lasting softness of the baked product, without, however,excessively affecting the structure of the native starch. This seems togenerate a hydrolysis product with a sticky consistency (e.g. thebranched maltodextrins with 20-100 glucose units produced by α-amylase)which would tend to impair this structure.

Consistent with the explanation given above, a preferred exoamylase foruse in the present process is one which exhibits exoamylase activity atand above the gelation temperature of starch (i.e. about 60-70° C.), asit has been found that the retrogradation of starch and consequently theprecipitation of amylose responsible for staling takes place at thistemperature. Another reason is that starch hydrolysis is facilitatedwhen the starch is gelatinized such that the swelling of the starchgranules caused by their uptake of liquid (water) liberated by thecoagulation of gluten loosens the normally tight structure of the starchgranules to make them more accessible to enzyme activity. This leads toa hydrolysis of the starch which is sufficient to retard retrogradationand to form adequate amounts of sugar without excessively modifying thenative starch, resulting in an improved water retention. Contrary tosuch a heat-stable exoamylase, cereal β-amylases inherently present inflour exhibit little starch hydrolytic activity in the process of bakingas they are inactive at the gelation temperature of starch. It should benoted that the exoamylases will be inactivated later in the bakingprocess, at temperatures above about 90° C. so that substantially noresidual exoamylase activity remains in the baked bread.

Preferred exoamylase enzymes are microbial exoamylases as these areeasier to produce on a large scale than exoamylases of, for instance,plant origin. An example of a suitable exoamylase is a maltogenicamylase producible by Bacillus strain NCIB 11837, or one encoded by aDNA sequence derived from Bacillus strain NCIB 11837 (the maltogenicamylase is disclosed in U.S. Pat. No. 4,598,048 and U.S. Pat. No4,604,355, the contents of which are incorporated herein by reference)This maltogenic amylase is capable of hydrolyzing 1,4-α-glucosidiclinkages in starch, partially hydrolyzed starch and oligosaccharides(e.g. maltotriose). Maltose units are removed from the non-reducingchain ends in a stepwise manner. The maltose released is in theα-configuration. In the U.S. Patents mentioned above, the maltogenicamylase is indicated to be useful for the production of maltose syrup ofa high purity. Another maltogenic amylase which may be used in thepresent process is a maltogenic β-amylase producible by Bacillus strainNCIB 11608 (disclosed in EP 234 858, the contents of which are herebyincorporated by reference).

For the present purpose, this maltogenic amylase may be added to flouror dough in an amount of 0.1-10,000 MANU, preferably 1-5000 MANU, morepreferably 5-2000 MANU, and most preferably 10-1000 MANU, per kg offlour. One MANU (Maltogenic Amylase Novo Unit) may be defined as theamount of enzyme required to release one μmol of maltose per minute at aconcentration of 10 mg of maltotriose (Sigma M 8378) substrate per ml of0.1 M citrate buffer, pH 5.0 at 37° C. for 30 minutes.

The dough may be leavened in various ways such as by adding sodiumbicarbonate or the like or by adding a leaven (fermenting dough), but itis preferred to leaven the dough by adding a suitable yeast culture suchas a culture of Saccharomyces cerevisiae (baker's yeast). Any one of thecommercially available S. cerevisiae strains may be employed.

The baked product is generally one made from, or at least containing acertain amount of, wheat flour as such baked products are moresusceptible to staling than products made from, for instance, rye flourdue to their airier structure. Thus, the baked product may be selectedfrom the group consisting of white bread, whole-meal bread, and breadprepared from mixtures of wheat and rye flour. Of course rolls or thelike made from the same type of dough are also included in thisdefinition.

In the present process, the exoamylase enzyme may be added to the doughin the form of a liquid, in particular a stabilized liquid, or it may beadded to flour or dough as a substantially dry powder or granulate.Granulates may be produced, e.g. as disclosed in U.S. Pat. No. 4,106,991and U.S. Pat. No. 4,661,452. Liquid enzyme preparations may, forinstance, be stabilized by adding a sugar or sugar alcohol or lacticacid according to established procedures. Other enzyme stablilizers arewell-known in the art.

In accordance with established practice in the baking art, one or moreother enzymes may be added to the flour or dough. Examples of suchenzymes are a-amylase (useful for providing sugars fermentable by yeastalthough it should only be added in limited quantities, for the reasonsgiven above), pentosanase (useful for the partial hydrolysis ofpentosans which increases the extensibility of the dough) or a protease(useful for gluten weakening, in particular when using hard wheatflour).

Also in accordance with established baking practice, one or moreemulsifiers may be added to the flour or dough. Emulsifiers serve toimprove dough extensibility and may also be of some value for theconsistency of the resulting bread, making it easier to slice, as wellas for its storage stability, as explained above. Examples of suitableemulsifiers are mono- or diglycerides, polyoxyethylene stearates,diacetyl tartaric acid esters of monoglycerides, sugar esters of fattyacids, propylene glycol esters of fatty acids, polyglycerol esters offatty acids, lactic acid esters of monoglycerides, acetic acid esters ofmonoglycerides, lecithin or phospholipids.

When the bread improver of the invention is provided as a substantiallydry formulation, it will typically contain the exoamylase insubstantially dry form. The enzyme may thus be in the form of a solidpowder or granulate which may be prepared in a manner known per se asindicated above. The term “substantially dry formulation” should, in thepresent context, be understood to mean that the formulation shouldappear as a dry and free-flowing powder and that the moisture content ofthe bread improver formulation should not exceed about 15%, andpreferably not exceed about 10%. When the bread improver is in the formof a semi-liquid preparation, the enzyme may also be incorporated inliquid form.

Apart from the exoamylase, the bread improver of the invention maytypically comprise one or more components selected from the groupconsisting of milk powder (providing crust colour), gluten (to improvethe gas retention power of weak flours), an emulsifier (such as one ofthose mentioned above), granulated fat (for dough softening andconsistency of bread), an oxidant (added to strengthen the glutenstructure; e.g. ascorbic acid, potassium bromate, potassium iodate orammonium persulfate), another enzyme (e.g. α-amylase, pentosanase or aprotease as explained above), an amino acid (e.g. cysteine) and salt(e.g. sodium chloride, calcium acetate, sodium sulfate or calciumsulfate serving to make the dough firmer).

It is at present contemplated that the exoamylase may be present in thebread improver in an amount of 1-5,000,000 MANU (as defined above) perkg of the bread improver, preferably 10-2,500,000 MANU, more preferably50-1,000,000 MANU, most preferably 100-500,000 MANU, and in particular1000-100,000 MANU of the exoamylase per kg of the bread improver. Inaccordance with conventional practice for the use of bread improvers,this may be added to flour in an amount of 0.2-10%, in particular0.5-5%, by weight of the flour.

The present invention is further illustrated in the following examplewhich is not in any way intended to limit the scope and spirit of theinvention.

EXAMPLE

White pan bread was prepared from the following ingredients

Wheat flour* 100% Water  52% Sodium chloride  2% Baker's yeast  2.5%*)commercial wheat flour of moderate quality (treated with ascorbicacid): ≈11% protein, ≈15% humidity

by mixing with a spiral mixer for 4 minutes at 140 rpm and for 3 minutesat 280 rpm (Speed of the spiral rotor). The dough temperature was 26° C.The dough was allowed to rise for 40 minutes at 34° C. and, afterdegassing and moulding, for 65 minutes at 34° C. The bread wassubsequently baked for 30 minutes at 230° C.

To the dough ingredients were added varying amounts of NOVAMYL™ (arecombinant maltogenic amylase encoded by a DNA sequence derived fromBacillus strain NCIB 11837, described in U.S. Pat. No. 4,598,048),Fungamyl 1600 S (a commercial α-amylase available from Novo-Nordisk a/s)and Veron F25 (a commercial α-amylase available from Rohm),respectively. The results appear from the following tables.

TABLE 1 NOVAMYL™, 1500 MANU/g Dosage in g/100 kg of flour Properties 06.7 13.3 27 53 107 Dough short short short short short short struc-struc- struc- struc- struc- struc- ture ture ture ture ture ture Volume100  99  99 100 100 101 index Crumb fine fine fine coarser structureCrumb 100 240 270 280 310 310 freshness (48 h) Crumb 100 160 200 230 270270 freshness (72 h) Crumb 100 160 390 425 500 580 freshness (96 h)Gummy no no no no no yes crumb

TABLE 2 Fungamyl™ 1600 S Dosage in g/100 kg of flour Properties 0 10 2040 80 160 Dough short pos. pos. dough dough dough struc- too too tooture soft soft soft Volume 100 102 107 107 106 106 index Crumb finefine/ fine/ coarser structure ripe ripe Crumb 100 240 280 290 330 320freshness (48 h) Crumb 100 145 240 230 280 290 freshness (72 h) Crumb100 200 250 530 650 675 freshness (96 h) Gummy no no no no/yes yes yescrumb

TABLE 3 Veron F25 Dosage in g/100 kg of flour Properties 0 10 20 40 80106 Dough short pos. pos. pos. pos. pos. struc- ture Volume 100 100 100102 102 102 index Crumb fine fine fine coarser structure Crumb 100 210210 210 235 210 freshness (48 h) Crumb 100 125 125 230 freshness (72 h)Crumb freshness (96 h) Gummy no no no no/yes yes yes crumb

It appears from the tables above that, compared to the use of Fungamyl1600 S and Veron F25, the addition of NOVAMYL™ to dough leads toimproved storage properties of the resulting bread without a concomitantgumminess of the crumb which only occurs a far larger dosage of theenzyme. NOVAMYL™ does not significantly change other dough or breadcharacteristics.

What is claimed is:
 1. A process for retarding the staling of a baked product comprising (a) adding a maltogenic α-amylase to either a flour that is then used to form a dough or directly to a dough wherein the maltogenic α-amylase is produced by Bacillus strain NCIB 11837 or is encoded by a DNA sequence derived from Bacillus strain NCIB 11837 and is added in an amount to retard the staling of the baked product; and (b) baking the dough to form the baked product.
 2. The process of claim 1, wherein the amount is from 0.1 to 10,000 MANU per kg of flour.
 3. The process of claim 2, wherein the amount is from 1 to 5000 MANU per kg of flour.
 4. The process of claim 3, wherein the amount is from 5 to 2000 MANU per kg of flour.
 5. The process of claim 4, wherein the amount is from 10 to 1000 MANU per kg of flour.
 6. The process of claim 1, further comprising adding a yeast culture to the dough.
 7. The process of claim 1, wherein the baked product is bread.
 8. The process of claim 7, wherein the baked product is white bread, whole-meal bread, or bread produced from mixtures of wheat and rye flour.
 9. The process of claim 8, wherein the baked product is white bread.
 10. The process of claim 1, wherein the baked product is made from or contains wheat flour.
 11. The process of claim 1, further comprising adding one or more other enzymes to the flour or dough.
 12. The process of claim 11, wherein the other enzyme(s) is/are α-amylase, pentosanase or a protease.
 13. The process of claim 1, further comprising adding one or more emulsifiers to the flour or dough.
 14. The process of claim 13, wherein the emulsifier(s) is/are mono- or diglycerides, polyoxyethylene stearates, diacetyl tartaric acid esters of monoglycerides, sugar esters of fatty acids, propylene glycol esters of fatty acids, polyglycerol esters of fatty acids, lactic acid esters of monoglycerides, acetic acid esters of monoglycerides, lecithin or phospholipids.
 15. A baked product produced by the process of claim
 11. 16. A process for producing a baked product comprising (a) adding a maltogenic α-amylase to a flour wherein the maltogenic α-amylase is produced by Bacillus strain NCIB 11837 or is encoded by a DNA sequence derived from Bacillus strain NCIB 11837; (b) preparing a dough from the flour; and (c) baking the dough to form the baked product.
 17. The process of claim 16, wherein the baked product is bread.
 18. The process of claim 17, wherein the baked product is white bread, whole-meal bread, or bread produced from mixtures of wheat and rye flour.
 19. The process of claim 18, wherein the baked product is white bread.
 20. The process of claim 16, wherein the baked product is made from or contains wheat flour.
 21. A baked product produced by the process of claim
 16. 22. A process for producing a baked product comprising (a) adding a maltogenic α-amylase to a dough wherein the maltogenic α-amylase is produced by Bacillus strain NCIB 11837 or is encoded by a DNA sequence derived from Bacillus strain NCIB 11837; and (b) baking the dough to form the baked product.
 23. The process of claim 22, wherein the baked product is bread.
 24. The process of claim 23, wherein the baked product is white bread, whole-meal bread, or bread produced from mixtures of wheat and rye flour.
 25. The process of claim 24, wherein the baked product is white bread.
 26. The process of claim 22, wherein the baked product is made from or contains wheat flour.
 27. A baked product produced by the process of claim
 22. 28. In a process for producing a baked product, the improvement comprising incorporating a maltogenic α-amylase to an ingredient used for producing the baked product, wherein the maltogenic α-amylase is produced by Bacillus strain NCIB 11837 or is encoded by a DNA sequence derived from Bacillus strain NCIB
 11837. 29. The process of claim 28, wherein the baked product is bread.
 30. The process of claim 29, wherein the baked product is white bread, whole-meal bread, or bread produced from mixtures of wheat and rye flour.
 31. The process of claim 30, wherein the baked product is white bread.
 32. The process of claim 28, wherein the baked product is made from or contains wheat flour.
 33. A baked product produced by the process of claim
 28. 34. A composition, comprising (a) a maltogenic α-amylase produced by Bacillus strain NCIB 11837 or is encoded by a DNA sequence derived from Bacillus strain NCIB 11837 and (b) one or more components selected from the group consisting of milk powder, gluten, an emulsifier, granulated fat, an oxidant, another enzyme, an amino acid and a salt.
 35. The composition of claim 34, wherein the maltogenic α-amylase is in liquid form.
 36. The composition of claim 34, wherein the maltogenic α-amylase is in dry form.
 37. The composition of claim 34, wherein the oxidant is ascorbic acid, potassium bromate, potassium iodate or ammonium persulfate.
 38. The composition of claim 34, wherein the other enzyme is α-amylase, pentosanase or a protease.
 39. The composition of claim 34, wherein the amino acid is cysteine.
 40. The composition of claim 34, wherein the salt is sodium chloride, calcium acetate, sodium sulfate or calcium sulfate. 